The study The study encompassed 50 patients who underwent 853 treatment sessions. To be included in the study, subjects had to have received a minimum of 10 injections, with the first treatment given before January 1999. The median number of treatments received per patient was 19 and the median interval from first to last treatment approached six years.
Through chart review and patient follow-up, only 10 adverse events were identified. They occurred in association with nine (1 percent) of the treatment sessions and involved eight patients — six had a single adverse event and two experienced two adverse events.
"From the results of this study, it seems we can conclude that no news is good news, and that potential candidates and practitioners alike can be reassured about the safety of appropriately administered botulinum toxin injection for cosmetic purposes," says Dr. Carruthers, clinical professor of dermatology, University of British Columbia, Vancouver.
Thanks to the remarkably favorable risk/benefit profile it demonstrated in clinical trials, botulinum toxin injection rapidly gained popularity after its marketing approval, and it became the most common cosmetic procedure performed in the United States. However, while its use became more widespread, concerns began to emerge about the safety of multiple treatments.
Funding for their retrospective trial was provided by an unrestricted grant from Allergan Inc., and they hired a private clinical research organization to identify and contact study subjects, extract and collect data, and perform the analyses.
"Insofar as was possible, we felt the methods used for this investigation allowed for a reasonably independent assessment of the long-term safety of botulinum toxin," Dr. Carruthers says.
Patients selected for inclusion in the analyses had been treated for facial rhytids and were Ž18 years of age. Individuals who met the eligibility criteria based on chart review were contacted to obtain informed consent.
The 50 patients ranged in age from 27 to 69 years, had a mean age of 43 years, and were predominantly women (92 percent) and white (92 percent). Their medical histories were unremarkable. About two-thirds of the subjects received treatments in three or more anatomic areas; the most common problems treated were glabellar rhytids (49 patients), crow's feet (35 patients) and forehead rhytids (32 patients).
Dose, interval not predictors The number of botulinum toxin injections administered per patient ranged up to 30, and the cumulative dose range was between 244 and 1,603 units (median, 690). The dose per session ranged from two to 110 units (median, 40). The mean dose of botulinum toxin for sessions associated with an adverse event was about 67 units.
The shortest total period of treatment in the study was 2.82 years, while the longest was almost nine years, although Dr. Carruthers observes some of the subjects had really been treated over an even longer interval considering that recordkeeping was limited for the earliest patients.
Statistical testing showed no relationship between the interval between treatment sessions or the number of treatments and the risk of adverse events.